Enhanced recovery of hydrocarbon through supercritical wet combustion, gravity stable in deep heavy-oil reservoirs

ABSTRACT

Method to enhance the recovery factor by injecting simultaneously or alternately air and water through a well, which is located in the top part of a heavy-oil reservoir showing dip and by producing fluids through a vertical or horizontal well, which is located in the formation lower part, resulting in a gravity stable burning front (GSAI or Gravity Stable Air Injection) at high temperature and pressure.

TECHNOLOGICAL SECTOR

This patent is related to the production and increase of recovery factorof heavy-oils in deep reservoirs by injection of air and water or steam.

STATE OF THE ART

One of the main problems in air injection, increased by major sandthicknesses and few vertical permeability barriers, is the displacementof this gas toward the top part of oil-bearing stratum, known in Englishas overriding combustion gases, caused mainly by the difference in gas-and oil-mobility. This causes a preferential channel for air, generallyin the top part of the reservoir, leaving a considerable sand zonewithout being altered by combustion and promoting a high production ofoxygen in producing wells

Therefore, this invention is intended to utilize the formation dip toenhance gravitational fluids segregation by maximizing the contact zonebetween water and air, increasing burning front area and producing astable advance thereof and higher time of cold production bydisplacement of original oil bank of the reservoir. Additionally, due tothe high pressure and temperature conditions present in the reservoir,the injected water will reach the supercritical condition in theproximity of the burning front enhancing transport properties and thephysicochemical improvement of the fluids, similarly to what isdescribed in US patent 2009/0206007 A1 and WO 2009/085436 A1.

The features of coke deposition in a reservoir are the basic parametersfor the design in the application of combustion process in situ. Thecoke is the fuel that supports the burning front resulting from thermalcracking and the distillation of crude oil near the combustion zone. Theamount of deposited coke is a function of API gravity, saturation andmobility of crude oil, the pressure and reservoir mineralogy, being morein heavy-oils, less mobile, under high pressure. (SPE 75207, JCPT Volume38, No.8). The coke deposition determines the quantity of air requiredfor the burning front advance; if the deposited coke is excessive, whichis often the case of heavy-oils, a big quantity of air is needed to burnit completely reducing the economic viability of the process andlimiting the applicability thereof to deep heavy-oils reservoirs.

A strategy to overcome these disadvantages is the process of wetcombustion, referred to in patents U.S. Pat. No. 3,520,363 and CA872041. In this process, the mechanism of coke formation and, therefore,the air requirement are reduced by improving the crude oil mobilitythrough transferred heat by steam. When the wet combustion is carriedout under supercritical conditions for water, part of the deposited cokereacts with water under such condition through reforming and water-gasshift (WGS) reactions, producing hydrogen and carbon oxides, asVostrikov et al. 2007 (Ind. Eng. Chem. Res. 46, 4710-4716; Energy &Fuels, 21, 2840-2845) shows. This reduces the amount of coke and,therefore, the oxygen consumption needed for its combustion.

A phenomenon contributing to the oxygen consumption reduction arisesbecause water under supercritical conditions behaves as an excellentorganic solvent. This behavior is well known in the state of art (J.Phys. Chem. B, 107, 12307-12314). Because of this property, water undersupercritical conditions passing through burning front dissolves crudeoil light fraction (maltenes) preventing these undergo thermal crackingby burning front and being converted to coke. Evidence thereof can benoted in experimental results of Watanabe et al. research, 2010 (TheJournal of Supercritical Fluids Volume 53, Issues 1-3, Pages 48-52).

Besides coke deposition, another parameter concerning air volume incombustion process in situ is the efficiency of oxygen utilization(Intevep, Procesos Térmicos de Extracción de Petróleo, 1987), whichdepends on the controlling reaction regime, which is defined by thetemperature range at which the reactions are performed. Most researchersput reaction regimes into two categories: low temperature reactions,LTO, and high temperature reactions, HTO (DOE. BC14994-21).

In an ideal combustion operation in situ for heavy-oils, coming firstreaction regime is HTO, wherein fuel reacts with oxygen at a temperaturehigher than 343° C. to produce carbon dioxide and water. At lowertemperatures (LTO) certain fraction of oxygen reacts with the crude oilto form oxygenated compounds (acids, ketone, alcohols, among others)assisting crude oil polymerization, increasing its viscosity, causingblocking problems in the reservoir (DOE., PC, 9 1 008-0374). This kindof condition can be reached if the oxygen supply is insufficient or ifthe heat losses in burning front are excessive, as it would happenduring a wet combustion with an excessive water supply.

One way of attenuating the LTO regime problem is improving the oxygentransport in combustion zone. This can be reached by wet combustionunder supercritical condition, wherein water shows the property ofdissolving oxygen in big quantities, as it is shown in the documentDOE., GA-C24239. On the other hand, as it is reported in the literature,fluids under supercritical conditions show very good diffusivity, highheat capacity and low viscosity. Accordingly, in a low permeabilityreservoir undergoing wet combustion process under supercriticalcondition, water can diffuse beyond the burning front transferring heatand reducing crude oil density and viscosity by dissolution. Thus,hydrocarbon mobility is significantly improved, even compared toconventional in situ wet combustion, with the additional benefit of abetter fluids distribution in the reservoir, even if this isheterogeneous.

Regarding heavy-oil quality improvement through treatment with waterunder supercritical condition, patents US 2010/0314583A1 and WO2009/085436A1 show two kinds of processes by which a crude heavy-oilwith significant sulfur, heavy metals and nitrogen content is treated,admixed with supercritical water in continuous reactors. As a result, animproved crude oil, with higher API gravity and lower sulfur, nitrogenand heavy metals content, is obtained. According to patent WO2009/085436A1 author, the API gravity increase is owing to crackingreactions, whereas the heavy metals and sulfur reduction is owing tometal or sulfur oxidation in hydrocarbon. Also, in the patent US2010/0314583A1 the author concludes that some sulfured components reactwith carbon monoxide to produce carbonic sulfide. The benefits shown inthese patents are also obtained in in-situ combustion processes due tothe fact that they are carried out with the same components (ACSC andcrude oil) under the same supercritical conditions of water.

DESCRIPTION OF THE FIGURES

FIG. 1 corresponds to a supercritical wet combustion process, gravitystable according to the present invention.

GENERAL DESCRIPTION OF THE INVENTION

This invention is intended to increase the recovery factor through airand water injection, simultaneously or alternately through a verticalinjection well located in the top part of heavy-oil reservoir formationshowing dip and producing fluids via vertical or horizontal well locatedin the lower part of the formation, causing a gravity stabilized burningfront (GSAI or Gravity Stable Air Injection) at high temperature andpressure.

Under high pressure and temperature conditions, present in thereservoir, either because of its initial condition or because of theprevious air or other fluid injection, the injected water reachessupercritical condition in the proximity of burning front, obtainingimprovement of its transport properties and its effect on presentreactions kinetics. These phenomena increase recovery efficiency andresult in a decrease of energetic requirements related to other in-situwet combustion processes.

This process provides the benefit of a less air requirement, bettercontrol of burning front advance, higher scanning efficiency and highercold production time for displacement of the reservoir original oil byproduced combustion gases and steam, latter effect resulting in a bettercontrol of the producing wells integrity.

The invention comprises the following aspects:

1. Simultaneous or alternated air and water injection through verticalinjection well in the top part of a reservoir showing dip

-   -   Air is injected through the injection well which is drilled in        the formation upper part.    -   Water is injected simultaneously or alternately. Water injection        starts once the existence of a stable burning front is        determined.

2. Oil production through a vertical producing well, located in thereservoir lower part and perforated in the formation lower part or ahorizontal well, the horizontal section thereof is in the producingformation lower part.

3. Generation of a burning front in the proximity of the injection wellface by spontaneous or artificial ignition.

4. Displacement of the burning front from the reservoir top part untilits lower part in a fluids gravitational segregation stable process.

5. Generation of water supercritical condition, injected in theproximity of the burning front owing to the reservoir condition or bypressurization thereof under pressures higher than 22.1 MPa andtemperatures higher than 380° C.

-   -   Under this condition water is hydrocarbon soluble in situ,        whereby the sweep efficiency of the zone located before the        burning front is increased. This causes the decrease of residual        oil saturation causing less coke generation and less air        requirement.    -   Water under this condition, in a hydrocarbon combustion process,        concerns present reactions causing less coke production and thus        less air requirement compared to typical combustion process,        either wet or dry.    -   Water under this condition and in the presence of minerals        present in the rock improves metals and sulfur removal from the        hydrocarbon, increasing produced fluid quality.

DETAILED DESCRIPTION OF THE INVENTION

The process requires drilling vertical injection well 3, located in thetop part of the structure and perforated in the formation upper part 4.Furthermore, drilling a vertical or horizontal producing well 8, locatedin the lower part of the structure and perforated in the formationlowest part 7. The process requires that the reservoir pressure behigher than water critical pressure, i. e. 22.1 MPa, otherwise theprocess starts with the fluid injection allowing reservoirpressurization.

Once pressure condition of the process is reached, ignition procedurestarts, which comprises an oxidizing gas injection 1 through injectionwell 3. Once the ignition has been reached, either artificially orspontaneously, the well is monitored in order to determine theavailability of a burning front, stable at HTO regime; afterwards,oxidizing gas and water injection 2 starts simultaneously oralternately. Oxidizing gas and water can be injected in variable ratiosdepending on well characteristics, either more oxidizing gas than wateror more water than oxidizing gas, or equal amounts of water andoxidizing gas.

Oxidizing gas can be air, oxygen or mixtures thereof, whereas water canbe fresh water, brine, formation water, sea water, carbondioxide-saturated water or mixtures thereof. In some instances, injectedwater can be in the form of steam.

Due to the well configuration and to the formation dip because of fluidsgravity segregation, injected oxidizing gas and produced hot gasesmigrate towards the formation upper part 5 and the heaviest fluids, aswater and hot oil, flow towards the lower part thereof 7 to be extractedthrough the boreholes 8 located in the lower part or in the producingwell horizontal section 9. These fluids go up through the producing wellto be brought to surface facilities 10.

Due to well configuration and with the help of gravity forces, theprocess according to the present invention produces a betterdistribution of oxidizing gas and a more stable advance of burning front6, preventing overriding effect, achieving higher sweep efficiency andthus higher recovery factor. Furthermore, supercritical conditionreached by water in the proximity of burning front 6 has a positiveinfluence on displacement phenomena, reaction mechanisms and kinetics,thus obtaining less air requirement and higher fluids qualityimprovement compared to a typical in-situ wet combustion process.

1. Method for enhanced heavy hydrocarbon recovery from deep reservoirswith dip, in which injection well in the reservoir top part andproducing well in the lower part have been drilled, comprises comprisingthe steps of: a) injecting oxidizing gas through the injection well; b)forming a burning front by spontaneous or induced oxidizing gasignition; c) monitoring the burning front until the stabilizationthereof is determined; d) injecting water and oxidizing gas throughinjection well; c) Extracting extracting fluid oil through producingwell, located in the formation lower part; wherein the well is under apressure higher than or equal to 22.1 MPa.
 2. The method according toclaim 1, wherein water and oxidizing gas are injected simultaneously. 3.Method The method according to claim 1, wherein water and oxidizing gasare injected alternately.
 4. Method The method according to claim 1,wherein a greater water proportion than that of oxidizing gas isinjected.
 5. The method according to claim 1, wherein a greateroxidizing gas proportion than that of water is injected.
 6. The methodaccording to claim 1, wherein equal amounts of water and oxidizing gasare injected.
 7. The method according to claim 1, wherein water isinjected in liquid form.
 8. The method according to claim 1, whereinwater is injected in form of steam.
 9. The method according to claim 1,wherein water is selected from the group consisting of fresh water,brine, formation water, sea water, carbon dioxide-saturated water ormixtures thereof
 10. The method according to claim 1, wherein oxidizinggas is selected from air, oxygen or mixtures thereof.
 11. The methodaccording to claim 1, wherein if the pressure inside the well is lowerthan 22.1 MPa, an inert gas is injected until the pressure inside thewell reaches at least 22.1 MPa before the step of oxidizing gasinjection.